Suze, a somewhat listless but deeply loyal teenage girl, comes into possession of a premium ticket to the Bianca Aquarium. She decides to go with her cheerful childhood friend, Lulu, to make the most of the rare opportunity. Inside the aquarium, they are personally guided by Chris, the wife of the aquarium’s director, and begin enjoying a day of extraordinary, beautifully crafted exhibits.

During the tour, Lulu suddenly vanishes without a trace. As Suze begins searching for her friend, the idyllic aquarium around her warps into a strange and hostile world that eerily resembles the original but is twisted and menacing. The elegant water tanks become traps, and the peaceful corridors turn into a labyrinth filled with threatening aquatic creatures. It is in this distorted space that Suze encounters Retro, a resolute woman clad in a military uniform and wielding a sword. Retro is also searching for someone—a girl named Kitty. Though initially brusque, Retro becomes an uneasy ally as Suze learns that the only way to survive and possibly escape this realm is to become one with the aquatic world itself.

The central setting is the Bianca Aquarium, a place that shifts from a fantastical showcase of marine life into a nightmarish limbo shaped by the power of a mysterious deep-sea stone. This stone granted a wish to Retro long ago: to create a world where everyone could live happily together. That wish warped reality, producing an unstable dimension where humans and fish blur together. People who wander into this space undergo a gradual transformation known as Creepy, losing their human forms and memories as they become creatures of the deep. The deeper Suze ventures, the more she risks the same fate.

The main characters include Suze, whose past trauma—a near-drowning incident as a child—gives her a unique affinity with water and the ability to transform into a jellyfish. Lulu is the lighthearted friend whose disappearance drives the entire search. Chris, the director's wife, is an enigmatic figure whose true nature is far from human: she is actually a Clione given human form by the deep-sea stone, acting out of obsessive love for the now-deceased director. Retro herself was once a great white shark that saved Suze years ago, and her wish to end the cycle of suffering drives the story's final decisions. Kitty is a fierce girl who serves Chris under duress, trying to save her sick younger brother.

The narrative unfolds through multiple arcs that deepen the mystery of the Creepy creatures, the nature of the deep-sea stone, and the cost of wishes. A pivotal revelation is that the gentle-looking Chris is a false copy: the real Chris became a monstrous orca-Creepy long ago. Retro’s wish, born from good intentions, created a world that traps and dissolves humanity. The final act involves a choice: whether to destroy the deep-sea stone, which would end the twisted world and all its inhabitants—including the innocent and the repentant—or to leave it intact and remain trapped. The story explores themes of sacrifice, the definition of genuine happiness, and whether a beautiful illusion is better than a painful truth.